1. Field of the Invention
The present invention relates to a ferrule as one portion of a plug side constituting an optical connector for making an optical connection.
2. Background Information
In the optical connector used in the optical connection of an optical fiber used in communication, etc., the optical fiber is inserted and fixed into the ferrule processed with respect to inside and outside diameters with high accuracy. Thereafter, the end face of a connecting portion of the optical fiber is polished in a convex spherical surface shape, and the optical connection is made by making the optical fibers come in physical contact with each other.
In the ferrule for inserting and holding such an optical fiber, there is a structure constructed by a cylindrical member, a cylindrical body for the ferrule arranged within the cylindrical member, and a flange member fixed to only the outer circumferential face of the cylindrical member.
Here, the conventional ferrule for inserting and holding the optical fiber will be explained in detail. FIG. 12 is a sectional view of the ferrule in the prior art.
As shown in FIG. 12(a), the ferrule 100 has a cylindrical member 110 having a through hole 101 extending therethrough in the axial direction, a cylindrical body 120 for the ferrule fitted to the side of a tip portion of the through hole 101 arranged in the cylindrical member 110 and inserting and holding the optical fiber, and a flange member 130 fixed to only the outer circumferential face of the cylindrical member 110.
For example, the cylindrical member 110 is formed by a metal such as stainless steel, etc., and the through hole 101 is formed in the cylindrical member 110 over the axial direction.
An insertion hole 102 of the cylindrical body for the ferrule for inserting and fixing the cylindrical body 120 for the ferrule by press fitting is formed on the tip portion side of this through hole 101. An optical buffered fiber insertion hole 103 for inserting and holding an optical buffered fiber formed by coating the outer circumference of the optical fiber is formed on the side of a rear end portion of the through hole 101.
The cylindrical body 120 for the ferrule fixed into the through hole 101 of the cylindrical member 110 is formed by hard ceramic and glass such as zirconia, etc. An optical fiber insertion hole 121 for inserting and holding the optical fiber is formed in the cylindrical body 120 for the ferrule over the axial direction. A taper portion 122 having an inside diameter gradually increased is arranged on the rear end portion side of this optical fiber insertion hole 121. No tip of the optical fiber inserted from the side of the optical buffered fiber insertion hole 103 abuts on the rear end face of the cylindrical body 120 for the ferrule, etc. by the taper portion 122 so that this tip is easily inserted into the optical fiber insertion hole 121.
The cylindrical member 110 is constructed by a large diameter portion 111 having a large outside diameter on the tip side, and a small diameter portion 112 having an outside diameter smaller than that of the large diameter portion 111 and arranged on the rear end side. A projecting portion 113 is projected in the small diameter portion 112 so as to have an outside diameter approximately equal to that of the large diameter portion 111 over the circumferential direction of the outer circumferential face.
The flange member 130 having a ring shape and fixed to only the outer circumferential face is arranged in this small diameter portion 112. For example, this flange member 130 is formed by a metal such as stainless steel, etc.
A through hole 131 is extended through this flange member 130 over the axial direction. A large diameter through hole 131a having an inside diameter slightly larger than the outside diameter of the projecting portion 113 is arranged on one end portion side of the through hole 131. A small diameter through hole 131b having an inside diameter slightly larger than the small diameter portion 112 of the cylindrical member 110 and slightly larger than the outside diameter of the projecting portion 113 is arranged on the other end portion side of the through hole 131. Namely, a step difference portion 131c is formed within the through hole 131 of the flange member 130 by the inside diameter difference between the large diameter through hole 131a and the small diameter through hole 131b. 
The flange member 130 is inserted from the large diameter through hole 131a side to the small diameter portion 112 side of the cylindrical member 110. The movement of the flange member 130 onto the large diameter portion 111 side with respect to the cylindrical member 110 is regulated by abutting the step difference portion 131c of the flange member 130 on the projecting portion 113 of the cylindrical member 110.
Thus, the movement of the flange member 130 onto the tip side with respect to the cylindrical member 110 is regulated. Accordingly, for example, when ferrules 100 are used in the optical connector, the tip faces of the ferrules 100 area butted on each other at a predetermined pressure by biasing the flange member 130 of each of the ferrules 100 optically connected by abutting their tip faces on each other on the tip face side. Therefore, it is possible to prevent the flange member 130 from being moved onto the tip face side with respect to the cylindrical member 110.
For example, four key grooves 132 of a concave shape are arranged on the outer circumferential face of the flange member 130, and regulate the movement in the rotating direction when the ferrule 100 is assembled into an unillustrated optical connector, etc. by the key grooves 132.
Such a ferrule 100 can be formed by fixing the cylindrical body 120 for the ferrule to the cylindrical member 110 by pressing fitting and adhesion, and then center-grinding and processing an assembly body constructed by this cylindrical member 110 and the cylindrical body 120 for the ferrule, and further performing centerless finishing and then fixing the flange member 130 by the press fitting and adhesion.
However, a problem exists in that the number of parts is large and cost is high in such a ferrule 100.
A problem also exists in that the ferrule 100 is heavy in weight since the cylindrical member 110 and the flange member 130 almost occupying the ferrule 100 are formed by a metal such as stainless steel, etc.
Further, a problem exists in that the grinding amount is large and a long working time is taken to perform the finishing operation with high accuracy since the center grinding work and the centerless finishing are performed after the cylindrical body 120 for the ferrule and the cylindrical member 110 are assembled.
Therefore, a ferrule constructed by the cylindrical body for the ferrule and the flange member fitted to the rear end portion of this cylindrical body for the ferrule without arranging the cylindrical member 110 is proposed.
As shown in FIG. 12(b), this ferrule 100A has a cylindrical body 120A for the ferrule having an optical fiber insertion hole 121A for inserting and holding an optical fiber and extending through the cylindrical body 120A for the ferrule over the axial direction, and a flange member 130A fitted to the rear end portion of the cylindrical body 120A for the ferrule.
For example, the cylindrical body 120A for the ferrule is constructed by ceramic such as zirconia, etc., and a taper portion 122A having an inside diameter gradually increased is formed in the rear end portion of the optical fiber insertion hole 121A extended and formed in the axial direction.
The flange member 130A is constructed by a metal such as stainless steel, etc., and an optical buffered fiber insertion hole 103A is formed so as to extend through the flange member 130A in the axial direction and be communicated with the optical fiber insertion hole 121A of the cylindrical body 120A for the ferrule.
A flange portion 133 projected in the circumferential direction is integrally arranged in the outer circumference of the flange member 130A, and a key groove 132A is arranged in this flange portion 133.
Such a ferrule 100A can be fixed and formed by fitting and adhering the flange member 130A to the rear end portion of the cylindrical body 120A for the ferrule by press fitting after the center grinding work and the centerless work are made with respect to the cylindrical body 120A for the ferrule.
The ferrule 100A can be made light in weight and reduced in cost by constructing the ferrule 100A by the cylindrical body 120A for the ferrule and the flange member 130A in this way.
Further, a time required to grind the cylindrical body 120A for the ferrule can be shortened by grinding the cylindrical body 120A for the ferrule constructed by a single member.
Since the cylindrical body for the ferrule constructed by such zirconia ceramic is formed by extrusion molding, the optical fiber insertion hole formed in the cylindrical body for the ferrule can be formed over the axial direction approximately at only the uniform inside diameter. However, in recent years, a method for forming the cylindrical body for the ferrule by the extrusion molding of a zirconia compound is established, and the degree of freedom of the shape formation of the optical fiber insertion hole formed in the cylindrical body for the ferrule is increased. Accordingly, the cylindrical body for the ferrule having the inside diameter of a so-called precise nozzle shape can be manufactured.
However, a problem exists in that manufacture cost is high in the ferrule formed by press-fitting and fixing the flange member to the rear end portion of the above cylindrical body for the ferrule since the flange member is formed by cutting a metal such as stainless steel, etc.
A problem also exists in that the ferrule is heavy in weight since the flange member is formed by the metal such as stainless steel, etc.
In consideration of such a situation, an object of the present invention is to provide a ferrule made light in weight and reduced in manufacture cost.